I'm looking for the C-API equivalent of the np.float64 function,
something that I could use inline in a Cython function.
I don't know how to write the function. Anyone have one sitting
around? I'd like to use it, if it is faster than np.float64 (np.int32,
np.float32, ...) in the Bottleneck package when the output is a
scalar, for example bn.median(arr, axis=None).